The most expensive number in engineering

O'Brien sheds a little light on one of the aspects of this: https://www.youtube.com/watch?v=UaPkSU8DNfY.

  GILORA: Starfleet code requires a second backup?
  O'BRIEN: In case the first backup fails.
  GILORA: What are the chances that both a primary system and its backup would fail at the same time?
  O'BRIEN: It's very unlikely, but in a crunch I wouldn't like to be caught without a second backup.

(But then I'm thinking, a species that mastered "stasis technology", commonly present in many sci-fi franchises, should eventually be able to make artifacts that can survive indefinitely, at least when not in operation.)

Those seem like obvious fantasy now, but from about the 1950s through the 1970s, a lot of serious people believed that there were undiscovered powers of the human mind that science was on the verge of discovering or confirming. Mental powers are therefore a common anachronism of sci fi from that era.

Most science fiction stories are going to feature some elements that are essentially unexplained and therefore act like magic in the story. I think most folks would consider 2001 to be science fiction but the powers of the monolith are at least as crazy and unexplained as what the Jedi can do.

I'm not a real Civil Engineer but I was a graduate one from 1991 - I'm now a IT bod. Anyway, Civ Eng uses established factors of safety or safety multipliers or safety factors or whatever. Structural steel uses 1.2 I recall - so you work out your worst case (in 100 years - look up tables) bending moment and mult by 1.2. Civ Eng is one thing and despite our bridges still failing after 2000 years of really solid knowledge. Tacoma Narrows (who knew the bloody things fly and shake) or London Millenium bridge - lol - shake, shake, shake the room - BOOM.

The thing about safety factors is that they need to be derived conclusively. In Civ Eng - wood is a bit wayward so the safety factor for it is quite large compared to steel.

I have no idea what you do for space thingies (yes I do) but I would expect my first 50 experiments to blow up - I need to explore the extremities.

If I ran a Space Agency I would say something like: "Soz, we are going to make some cracking firework displays first and then we will know what to avoid."

Many comments here relate more to one-off design. There is also the medium-high-volume manufacturing end. There, a prototype run might be in the dozens or hundreds of units, more than the entire manufacturing run in other heavy industries.

As the OP hints, "safety factor" is not the only term to use. A design margin (including reduction in margin) can be planned with one or more motivations: safety, reliability, weight, volume, reduced BOM costs, unit costs of repair, fleet costs of repair, logistic and warehouse costs of parts for repair, planned obsolescence, and so on.

Probabilistic design, also realized through "Monte Carlo" analysis, can take into account multiple simultaneous non-linearity in various models, where symbolic or formula-based analysis might fail.

For example (and roughly speaking), if one has millions of miles of over-the-road data, say of wheel-to-road forces or geometric road or track profiles, then one might manage to calibrate the following together: 1) a specific vehicle physical model, including parts tolerances and probabilistic discrete flaws; 2) material cycle-fatigue damage properties; and 3) some set of Weibul-distribution-like parameters as an intermediate in predicting failure rates and "lifetimes." .. AFAIK the kind of business analysis one might do could include predicting how many parts one should overproduce and warehouse (in a one-time batch) to service in-warranty and post-warranty repairs out to N years.

At that scale it can also become sociological. "Safety margin" is a loaded term when it comes to liability and imprecision in intent. You reduced the safety margin, as it says right here?!!

Not a bad article, but there could be a whole article on ramifications of different margin-related wording, high-N statistics, and explicit accounts of simultaneous goals.

You build people movers, and wonder about safety factor???

WTF!!!

There's also service factor. Protip: Multiply them both please.